Device for accelerating electrons to very high velocities



Marsh H2, 1940. PENNEY 2,193,62

DEVICE FOR ACCELERATING ELECTRONS TO VERY HIGH VELOCITIES Filed May 6,1938 2 Sheets-Sheet 2 INVENTOR Gay/0rd M/ Pen/2% Patented Mar. 12, 1940.

STATES PATENT OFFICE DEVICE FOR ACCELERATING ELECTRONS TO VERY HIGHVELOCITIES Pennsyl Application May 6, 193a, Serial No. 206,379 6 Claims.(01. zen-27.5)

The invention relates to devices for accelerating electrons to very highvelocities.

An object of the invention is to provide means for acceleratingelectrons to very high velocities prior to impinging them upon a target.

Other objects and advantages of my invention will be apparent from thefollowing description and drawings, in which:

Figure 1 is a view, partly in elevation and partly in cross-section, ofa device embodying my invention; I

Fig. 2 is a modification of Fig. 1;

Fig. 3 is a view in cross-section through the tube of Fig. 1;

Fig. 4 is a cross-sectional view similar to that of Fig. 3, withmodifications therein;

Fig. 5 is a cross-section on lines V-V of Fig. 3;

Fig. 6 is a View, partly in elevation and partly in cross-section, of adetailed modification of Fig. 1; and

Fig. 7 is a diagrammatic view of a preferred circuit for applying energyto the device.

In my invention for accelerating electrons to a high velocity, I providemeans for keeping the electrons from wandering to the walls of thedischarge tube and also for accelerating the electrons to high velocity.I provide an annular vacuum accelerating chamber l9, which may have thesquare cross-section illustrated in Fig. 1, or the circularcross-section illustrated in Fig. 2. Other configurations may beutilized.

I provide a magnetic flux perpendicular to the plane of this annularchamber, which may be accomplished by having annular magnetic polepieces H and i2 above and below the chamber, which pole pieces areconnected to the core [3 of the electromagnet It. The magnetic fieldfrom this magnet acts to make the moving electron follow a circularpath.

I also provide a second magnetic circuit to produce a flux through thecentral opening of this annular chamber, which may be provided by theelectromagnet l5 having the poles l6 and I! extending into the annularopening. The magnetic fields from both of these electromagnets arechanged in proportion to maintain the radius of the electron pathsubstantially constant.

I also provide means to keep the particle focused. This can be provided,as illustrated more clearly in Fig. 5, by pole faces l8, i9, 26 and 25.These pole faces provide an electrostatic field which tends to repel theelectrons from the walls. The pole faces 58 and 119 are preferablypositive, and the pole faces 26 and 2t are preferably negative. Thenegative electrodes 28 and 2t repel the electrons, and the radial,centrifugal and electromagnetic forces keep the electrons from reachingthe positive electrodes I 8 and i9.

If the electrons are accelerated by an increasing magnetic flux withboth magnetic fields starting from zero at the same time, and theelectron starts from rest, then the flux densities for a given radius orpath in the two fields must bear a given ratio, and if these fluxes aremaintained in this ratio while increasing, the radius will remainpractically constant.

In Fig. 2, the air gap of the magnetic field of pole pieces It and [2becomes smaller as the radius increases, so that the flux increases withthe radius at the desired circle of rotation. This has the efiect ofdecreasing the radius whenever the electron arrives at a radius largerthan the desired circle, and conversely increasing the radius wheneverthe electron gets inside of the desired circle. The flux density at thecircle traveled by the electron is One-half'the average flux densityover the area enclosed by said circle.

In Fig. 2, a stronger electrostatic field of the same frequency andphase as the magnetic field is applied to the electrodes I8, I5, 20' andH which have been shown as arcs of cylinders in place of the planes inFig. 1. This stronger electrostatic field will correct any instabilityin regard to the plane of rotation.

If the electrons start from rest at the instant of zero flux, they arestrictly in equilibrium at a given radius." However, I also providemeans so that the electrons will have avelocity corresponding to thatwhich they would have had it they had started from rest with the fluxequal to zero. This velocity of the electrons is preferably accomplishedby the means disclosed in Figs. 3

and 4. A hot cathode 25 is preferably utilized as a source of electrons,and this cathode is preferably in an arm 26 opening into the main partof the vacuum chamber Ill. The electrode 18 lining the wall is suitablybroken for the entrance of this electron. Perforated discs 21 of anynumber are utilized for concentrating the electrons in the centralportion of the arm 26. also located in the arm 26 to give the electronits acceleration by means of a surge applied thereto in order that theelectron will reach the annular portion of the chamber it with thedesired velocity.

Another arm 30 is also located in a tangential relationship with aportion of the accelerating chamber H3 and contains a target 3!, uponwhich the electron will impinge after it has reached Electrodes 28 arethe desired high velocity. An electrode 32 is placed adjacent theopening of the arm into the annular chamber l0, andhas a suitable chargeapplied thereto at the proper moment to pull the electron or electronsfrom the annular orbit towards the target.

In Fig. 4, I have illustrated further modifications of the device. Theelectrostatic electrodes IS, IS, 20' and 2t are preferably spaced aroundthe annulus in arc sections as illustrated by 2|. The other threeelectrodes have the relation to 25' as shown in Fig. 2. These sectionsare preferably symmetrically spaced and as shown, extend about 40 to 45of annular length around the chamber. In the space intermediate thesections of the electrode, I preferably place small electrodes 4| in theform of rings to aid in keeping the electron, if necessary, in thecenter of the annular ring. These electrodes 4| are charged positivelyduring the accelerating period with respect to the rest of the apparatusand act as a lens to correct any deviation from direction of thecircular path about the desired center.

In order to get the electrons into the magnetic field at the proper timeand with the desired direction, radius and velocity, I provide anelectrode 43 at the juncture of arm 26 and the annular chamber. Anelectron shot into a uniform magnetic field, if it can go from no fluxto uniform flux, will travel in a circle which is tangent to theoriginal direction at the point where the electron enters the field. Animpulse voltage is applied to the electrode 43 and the electrostaticfield is sufilcient to counteract the magnetic field as the electronenters the annular chamber. This impulse positive voltage is applied atthe instant just past the flux zero when the electron beam should havethe proper velocity to travel in the circular path of the center of theannular chamber. The purpose of this electrostatic field is tocounteract the magnetic field as the electrons enter, so that theelectrons tend to travel about the axis of the annular chamber and notabouta center perpendicularto the motion at initial entrance to theflux. The electrode 43 is preferably at an angle as disclosed so thatthe effect is Weak when the electron is in the fringing flux andincreases as the electron enters" the stranger field.

In order to remove the electrons from the circular orbit at maximumvelocity and in the desired direction, I provide, in addition to theelectrode 32, a coil 44 to which an impulse of current is applied at ornear the maximum electron velocity. The coil consists of two parts inseries one above and one below the vacuum chamber. At the instant ofmaximum electron velocity, an impulse current, preferably from a chargedcondenser and released by triggering grid-glow tube, is sent throughcoil 44 and in direction to oppose the main flux which first displacesthe center and then deflects the electrons into tube 34' which containstarget 35. Coil 44 should be adjustable in position and the optimumposition determined experimentally. A mechanically moving laminated ironpiece might be instead, or in addition, to be suddenly moved adjacent tothe tube at a position adjacent electrode 32', so as to reduce the fiuxdensity over a small region which first shifts the center of rotationand finally causes the electron to leave the annular chamher.

The arm 34" in Fig. 4 is also disclosed as substantially tangent to theadjacent curved end of the electrode 2| The target 35 is also disclosedas perpendicular to the path of the electron. If desired, perforatedscreens similar to 2'! may be placed so that only electronssubstantially axially aligned with the target will impinge thereon.

I also contemplate utilizing one magnetic field instead of the twofields disclosed in Figs. 1 and 2. In this case, I provide the two polefaces 36 and 31 with projections 38 and 39 into the central opening ofan annular chamber 40 set in with the fiat portion surrounding theprojection 38 on pole piece 36, and the flat portion 46 surrounding theprojection 39 on the pole piece 31, as illustrated in Fig. 6. Thisconstruction provides for the magnetic flux through the center and alsothrough the annular chamber 40.

In Fig. 7, is a diagrammatic illustration of a preferred circuit forapplying energy to the device. A sourceof alternating current 50supplies a frequency preferably as high as possible that will notproduce distortion. 500 to 1000 cycles are desirable for this source anda larger number may possibly be used. This frequency is applied to thesingle coll 5| that supplies the energy for the magnetic flux for thepole pieces 36 and 31 of Fig. 6, or it may supply both coils l4 and I5of Figs. 1 and 2. The source 50 may be of any desired voltage. A branch52 from this source preferably supplies the positive charge through atapped transformer 53 to the interior electrodes l8 and I9 and thenegative charge to the electrodes 20 and 2| as illustrated on theleft-hand side of the view through the tube and pole pieces 36 and 31.The source 50 also preferably supplies the charge for the electrodes onthe right-hand side from a branch 54 through a tapped transformer 55.The charge for the ring electrodes 4| may be similarly applied by atapped transformer and have a return through electrodes 20, 2| to thetransformer. Phase shifters 56 and 51 are preferably put in the branchcircuits 52 and 54' and adjusted with tests by the well-known exploringcoil and oscillograph so that the electrostatic field in the annulartube is in phase with and of the same frequency as the magnetic field.

The electricity and magnetic fields applied to the device may be ofintensities depending, among other things, on the size and quality ofthe parts in a manner that will be apparent to those skilledin the art.Accordingly, the following values are to be taken in an illustrative andnot in a limiting sense.

The ring electrodes 4| I prefer to have a length approximately 5% of theinner diameter of the annular chamber. The voltage applied to these ringelectrodes and the plate electrodes is preferably such as to provide apotential gradient of 50,000 to 100,000 volts per centimeter adjacentthe edges of the electrodes and an average potential gradient of 5000 to20,000 volts per centimeter between these electrostatic electrodes. Ifthe positive and negative electrodes l8, I9, 20 and 2| are approximatelyin the form of an inch square, there may be applied a difference of20,000 volts between these positive and negative electrodes. Likewise, apotential difference of 30,000 to 40,000 volts may be applied betweenthe ring electrode 4i and the negative electrode 20.

Iron for the magnetic circuit should be well laminated 'and of the bestcommercial grade. Near the pole faces especially great care should betaken to secure a uniform density of iron and a true surface of polefaces because uniformity of flux over the desired circle of rotation isvery I important. circular.

As a specific example of dimensions in regard to Fig. 7. the annularchamber may be approximately one inch in overall diameter and the biasedslopes of the adjacent pole pieces having as close to an average spacingof one inch or the diameter of the tube as possible. The slopes may befrom 1 to 8". The spacing between the pole pieces axially of the ring isapproximately of an inch. These inner pole faces may be approximately 3%inches in diameter and the overall diameter of the legs of theelectromagnet may be from 6 to 6%; inches. Such values are, of course,illustrative and not limiting.

In the operation of the device, an electron is shot into the tube whenthe magnetic flux passes through zero and this electron is acceleratedwhile the flux builds up to its maximum and, at this time, the electronis directed against the target. Electrons may also be shot into the tubeand those arriving at the center line when the magnetic flux is zeroaccelerated and the the rest disregarded.

ll lhiie l have disclosed certain preferred embodiments of my invention,it is apparent that many modifications may be made in the form,arrangement and number ofelements disclosed therein. Accordingly, Idesire only such limitations as are necessitated by the prior art.

I claim as my invention:

i. In combination with an annular evacuated chamber, means forprojecting charged electrical particles tangentially into said annularchamber, means for accelerating said particles circumferentially of saidchamber, and means for producing a magnetic field traversing saidchamber substantially perpendicular to the principal plane thereof. thesaid magnetic field increasing in intensity as the outer periphery ofthe annulus is approached.

2. In combination with an annular evacuated chamber, means forprojecting charged electrical particles tangentially into said annularchamber, means for accelerating said particles circumfer- The pole is,of course, preferably entially of said chamber, and means for producingan electric potential gradient sloping from points in said chamber whichare laterally displaced from the principal plane thereof toward saidprincipal plane, the polarity of said potential gradient being such asto accelerate said charged particles toward said principal plane.

3. In combination with an annular evacuated chamber, means forprojecting charged electrical particles tangentially into said annularchamber,

means for accelerating said particles circumferentially of said chamber,means for producing an electric potential gradient sloping from pointsin said chamber which are laterally displaced from the principal planethereof toward said principal plane, the polarity of said potentialgradient being such as to accelerate said charged particles toward saidprincipal plane, and means for producing a magnetic field travering.said chamber substantially perpendicular to the principal plane thereof,the said magnetic field increasing in intensity as the outer peripheryof the annulus is approached.

4. In combination with an annular evacuated chamber, means forprojecting charged electrical particles tangentially into said annunlarchamber, means for producing a varying magnetic field through thecentral aperture of the annulus, and means for producing a magneticfield normal to the principal plane of said annulus and traversing saidchamber, said magnetic field increasing in intensity as the outerperiphery of said annulus is approached.

5. In combination with an annular evacuated chamber, means forprojecting charged electrical particles tangentially into said annularchamber, means for producing a varying magnetic field through thecentral aperture of the annulus,

means for producing a magnetic field normal tothe principal plane ofsaid annulus and traversing said chamber, said magnetic field increasingin intensity as the outer periphery of said annulus is approached, apair of conductors at points substantially displaced respectively onopposite sides of said principal plane, at least one annular conductornear the wall of said chamber in the region of said principal plane, andmeans for imparting to said pair of conductors an electrical potentialrelative to the last named conductor which is of the same polarity assaid charged particles.

6. In combination with an annular evacuated chamber, means forprojecting charged electrical particles tangentially into said annularchamber, means for producing a varying magnetic field through thecentral aperture of the annulus, means for producing a magnetic fieldnormal to the principal plane of said annulus and traversing saidchamber, said magnetic field increasing in intensity as the outerperiphery of said annulus is approached, and means for-causing thesecond said magnetic field to vary in syncbronism with the first saidmagnetic field.

GAYLOR'D W. PM.

